Any destructive emotion can be countered . Since Anger is a destructive emotion which affects our mind and soul, its important to find out which emotion will help to counter this destructive emotion. If anger causes suffering, ill health then we have to find out a antidote which will oppose this emotion and cure us. And the antidote for this Compassion. Both Anger and Compassion are emotions, but they have a different view of seeing the same object. Thy are poles opposite when looking at the same object.
When you feel hot, you try to do everything to make your body cool down. You might open the window, switch on the Air condition or the fan. Ice pack, put a wet cloth on your face etc etc. Just as Cold opposes heat, compassion opposes anger and creates a pleasant mental state while handling the predicaments of life. So when you develop compassion inside you, anger inside you decreases.
You can imagine yourself as a sick person afflicted by Lust, Hatred and Anger. The only antidote available to cure the illness you have been afflicted is Compassion. So when you start your Transformative practices, it acts as an antidote to your mind and helps in creating a sense of well being for yourself and for those around you.
We should always think that for the well being of self and those around us, love and compassion should become part of us. This will help us in finding our true purpose of life and in creating a good pathway for our own spiritual development.